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| United States Patent |
5,512,353
|
|
Yokotani
, et al.
|
April 30, 1996
|
Ceramic substrate for an electronic circuit
Abstract
The ceramic substrate for electronic circuit of the present invention
comprises a ceramic layer and a conductive layer which is patterned on the
ceramic layer, wherein the conductive layer comprises copper or an alloy
containing copper as its main component. The ceramic layer entirely
comprises a complex oxide or an oxide solid solution containing copper
element and at least one component excluding copper element. Moreover, the
ceramic layer is insulated.
| Inventors:
|
Yokotani; Yoichiro (Suita, JP);
Ando; Hamae (Neyagawa, JP);
Kugimiya; Koichi (Toyonaka, JP)
|
| Assignee:
|
Matsushita Electric Industrial Co., Ltd. (Osaka, JP)
|
| Appl. No.:
|
263157 |
| Filed:
|
June 20, 1994 |
Foreign Application Priority Data
| Current U.S. Class: |
428/210; 257/E23.072; 257/E23.077; 361/321.1; 361/321.2; 428/432; 428/433; 428/901; 501/134; 501/135 |
| Intern'l Class: |
B32B 009/00 |
| Field of Search: |
428/210,432,433
361/321.1,321.2
501/134,135
|
References Cited
U.S. Patent Documents
| 3075860 | Jan., 1963 | Veres | 174/259.
|
| 4503090 | Mar., 1985 | Brown et al. | 427/96.
|
| 4714570 | Dec., 1987 | Nakatani et al. | 252/518.
|
| 4724182 | Feb., 1988 | Kato et al. | 428/901.
|
| 4863683 | Sep., 1989 | Nakatani et al. | 419/10.
|
| 4885661 | Dec., 1989 | Yokotani et al. | 361/321.
|
| 5004715 | Apr., 1991 | Hakotani et al. | 501/136.
|
| 5036167 | Jul., 1991 | Kasai | 174/258.
|
| Foreign Patent Documents |
| 0332457 | Oct., 1989 | EP.
| |
| 51-11793 | Apr., 1976 | JP.
| |
| 51-11795 | Apr., 1976 | JP.
| |
| 51-26640 | Aug., 1976 | JP.
| |
| 62-031906 | Feb., 1987 | JP.
| |
| 1-258307 | Oct., 1989 | JP.
| |
| 1-293595 | Nov., 1989 | JP.
| |
| 2303107 | Dec., 1990 | JP.
| |
Primary Examiner: Ryan; Patrick J.
Assistant Examiner: Lee; Kam F.
Attorney, Agent or Firm: Panitch Schwarze Jacobs & Nadel
Parent Case Text
This is a continuation of application Ser. No. 07/809,985, filed Dec. 18,
1991, now abandoned.
Claims
What is claimed is:
1. A ceramic substrate for a multilayered electronic circuit comprising
plural ceramic insulated layers, and plural conductive layers which are
patterned on the ceramic layers, the ceramic insulated layers and
conductive layers being laminated alternately,
wherein the conductive layers comprise metallic copper or an alloy
containing metallic copper as its main component, and
wherein the ceramic layers entirely comprise a complex oxide or an oxide
solid solution containing copper and at least one component other than
copper,
wherein the complex oxide or the oxide solid solution is prepared by using
oxide containing copper as a starting material, whereby the diffusion rate
of the copper oxide from the conductive layers to the ceramic layers can
be lowered, and
wherein each of the complex oxide and the oxide solid solution contains at
least one element selected from the group A consisting of strontium,
barium, calcium, and lead, and at least one element selected from the
group B consisting of tungsten, niobium, and tantalum, so as to form a
complex perovskite structure phase.
2. A ceramic substrate for electronic circuit according to claim 1, wherein
the content of a copper oxide component in the ceramic layers is in the
range of 0.3% to 5% by weight in terms of CuO.
3. A ceramic substrate for electronic circuit comprising a ceramic
substrate, a conductive layer which is patterned on the ceramic substrate
and comprises copper or an alloy containing copper as its main component,
at least one insulated layer formed so as to cover a portion of the
conductive layer, and another conductive layer which is patterned at least
on the insulated layer and comprises copper or an alloy containing copper
as its main component,
wherein the insulated layer entirely comprises a complex oxide or an oxide
solid solution containing copper and at least one component other than
copper,
wherein the complex oxide or the oxide solid solution is prepared by using
oxide containing copper as a starting material, whereby the diffusion rate
of the copper oxide from the conductive layers to the insulated layers can
be lowered, and
wherein each of the complex oxide and the oxide solid solution contains at
least one element selected from the group A consisting of strontium,
barium, calcium, and lead, and at least one element selected from the
group B consisting of tungsten, niobium, and tantalum, so as to form a
complex perovskite structure phase.
4. A ceramic substrate for electronic circuit according to claim 3, wherein
the content of a copper oxide component in the insulated layer is in the
range of 0.3% to 5% by weight in terms of CuO.
5. A ceramic substrate for a multilayered electronic circuit according to
claim 1, wherein copper in the ceramic layers does not exist as a metal or
as an oxide containing a copper element alone, as confirmed by an X-ray
diffraction analysis.
6. A ceramic substrate for a multilayered electronic circuit according to
claim 1, wherein the starting material is prepared by mixing, calcining
and grinding.
7. A ceramic substrate for a multilayered electronic circuit according to
claim 1, wherein the metallic copper or the alloy containing metallic
copper as its main component does not partially diffuse from the
conductive layer into the ceramic layer.
8. A ceramic substrate for a multilayered electronic circuit according to
claim 1, wherein the ceramic layer is prepared from a composition of the
formula:
Sr.sub.0.5 Ca.sub.0.5 (Cu.sub.1/4 Nb.sub.3/4).sub.0.05 (Mg.sub.1/3
Nb.sub.2/3).sub.0.90 (Zn.sub.1/2 W.sub.1/2).sub.0.05 O.sub.3 + 2 wt % LiF.
9. A ceramic substrate for a multilayered electronic circuit according to
claim 1, wherein the ceramic layer is prepared from a composition of the
formula:
Pb.sub.0.65 Ca.sub.0.40 (Cu.sub.2/5 W.sub.3/5).sub.0.06 (Mg.sub.1/3
Ta.sub.2/3).sub.0.90 (Ni.sub.1/2 W.sub.1/2).sub.0.05 O.sub.3.
10. A ceramic substrate for a multilayered electronic circuit according to
claim 2, wherein the ceramic layer is prepared from a composition of the
formula:
Al.sub.2 O 55 mol % + SiO.sub.2 20 mol % + MgO 10 mol % + ZnO 10 mol % +
Li.sub.2 O 3 mol % + CuO 2 mol %.
11. A ceramic substrate for a multilayered electronic circuit comprising
plural ceramic insulated layers, and plural conductive layers which are
patterned on the ceramic layers, the ceramic insulated layers and
conductive layers being laminated alternately,
wherein the conductive layers comprise metallic copper or an alloy
containing metallic copper as its main component,
wherein the ceramic layers comprise a copper element, and the copper
element does not exist as a metal or as an oxide containing copper element
alone, as confirmed by x-ray diffraction analysis,
wherein the ceramic layers contains at least one element selected from the
group A consisting of strontium, barium, calcium, and lead, and at least
one element selected from the group B consisting of tungsten, niobium, and
tantalum,so as to form a complex perovskite structure phase.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ceramic substrate for electronic circuit
using, as a conductive metal, copper or an alloy containing copper as its
main component and a method for producing the same. More particularly, it
relates to a ceramic substrate for electronic circuit in which a special
composition is used for a ceramic layer in a ceramic substrate for
multilayer electronic circuit or for an insulated layer in a ceramic
substrate for printed electronic circuit.
2. Description of the Prior Art
In recent years, there has been a great demand for a ceramic substrate for
electronic circuit since it is required that a circuit element or a
semiconductor device be highly integrated and a circuit substrate be made
highly reliable.
As a ceramic substrate for electronic circuit, there are a substrate for
multilayer electronic circuit obtained by patterning a conductive layer on
unfired ceramic green sheets, laminating the resulting green sheets,
followed by firing them together; a substrate for printed electronic
circuit obtained by forming a conductive layer, an insulated layer, and
another conductive layer on a sintered ceramic substrate in this order so
that the insulated layer is sandwiched between both conductive layers; and
the like. The substrate for multilayer electronic circuit is used as a
substrate which is required to be highly integrated such as a circuit
substrate on which an LSI chip or the like is mounted. The substrate for
printed electronic circuit is used as a substrate of a hybrid IC or the
like in which functional elements such as a resistor and a capacitor are
further formed on the substrate.
In the past, as a ceramic material used for ceramic substrates for
electronic circuit, an alumina type material, a glass ceramic type
material, or the like has been used. In particular, as a method for a
ceramic substrate similar to the present invention, Japanese Patent
Publication Nos. 51-11795, 51-11793, 51-26640, etc. disclose materials
obtained by adding a copper oxide to alumina is used.
As a material for a conductive layer, tungsten, molybdenum, or the like is
used in the case of a substrate for multilayer electronic circuit; and a
gold or silver type material is used in the case of a ceramic substrate
for printed electronic circuit. However, tungsten, molybdenum, or the like
has a large electric resistance, causing problems when wiring is made
thin. Moreover, there are the problems in that gold is expensive and
silver is likely to migrate.
In order to solve the above-mentioned problems, a ceramic substrate for
electronic circuit in which inexpensive copper having a low resistance is
used for a conductive layer has been proposed. When a conductive layer and
a ceramic layer in the case of a substrate for multilayer electronic
circuit are simultaneously fired, or when a conductive layer and an
insulated layer in the case of a substrate for printed electronic circuit
are simultaneously fired, using e base metal such as copper as the
conductive material, a binder in the ceramic layer or the insulated layer
and the conductive layer is burnt out by adding water vapor in an inert
gas atmosphere in which the conductive layer is not oxidized, and then the
ceramic layer or the insulated layer and the conductive layer are fired in
an inert gas atmosphere. However, according to this method, the binder is
not sufficiently burnt out, causing problems such as remaining carbon. For
the purpose of solving this problem, as described in Japanese Laid-Open
Patent Publication No. 61-26293, a method comprising the steps of: forming
the conductive layer with a copper oxide; burning out the binder in the
ceramic layer or the insulated layer and the conductive layer in air;
metallizing the conductive layer alone at a low temperature by reduction;
and firing the ceramic layer or the insulated layer and the conductive
layer in an inert gas atmosphere.
Moreover, as described in U.S. Pat. No. 4,503,090, a method comprising the
steps of: diffusing a copper component oxidized from the conductive layer
into the ceramic layer on the lower part of the conductive layer; and
forming a reaction layer of copper oxide and a ceramic component on the
lower part of the conductive layer has been proposed.
However, in a conventional ceramic substrate for electronic circuit having
the conductive layer comprising copper or an alloy containing copper as
its main component, the copper oxide is partially diffused from the
conductive layer to the ceramic layer in the case of the substrate for
multilayer electronic circuit or in the insulated layer in the case of the
substrate for printed electronic circuit in the course of the production.
Thus, defects are caused due to the difference in the firing conditions
between the portion in which the copper oxide is diffused and the other
portion.
SUMMARY OF THE INVENTION
The ceramic substrate for electronic circuit of this invention, which
overcomes the above-discussed and numerous other disadvantages and
deficiencies of the prior art, comprises a ceramic layer and a conductive
layer which is patterned on the ceramic layer, wherein the conductive
layer comprises copper or an alloy containing copper as its main
component, and wherein the ceramic layer entirely comprises a complex
oxide or an oxide solid solution containing copper element and at least
one component excluding copper element, and the ceramic layer is
insulated.
In a preferred embodiment, the ceramic layer comprises an oxide selected
from the group consisting of a complex oxide, an oxide solid solution, and
an oxide complex, the oxide complex containing at least one oxide selected
from the group consisting of the complex oxide and the oxide solid
solution as its component, wherein each of the complex oxide, the oxide
solid solution, and the oxide complex contains copper element, at least
one element selected from the group A consisting of strontium, barium,
calcium, and lead, and at least one element selected from the group B
consisting of tungsten, niobium, and tantalum.
In a preferred embodiment, the content of a copper oxide component in the
ceramic layer is in the range of 0.3% to 5% by weight in terms of CuO.
A ceramic substrate for electronic circuit comprises a ceramic substrate, a
conductive layer which is patterned on the ceramic substrate and comprises
copper or an alloy containing copper as its main component, at least one
insulated layer formed so as to cover a portion of the conductive layer,
and another conductive layer which is patterned at least on the insulated
layer and comprises copper or an alloy containing copper as its main
component, wherein the insulated layer entirely comprises a complex oxide
or an oxide solid solution containing copper element and at least one
component excluding copper element.
In a preferred embodiment, the insulated layer comprises an oxide selected
from the group consisting of a complex oxide, an oxide solid solution, and
an oxide complex, the oxide complex containing at least one oxide selected
from the group consisting of the complex oxide and the oxide solid
solution as its component, wherein each of the complex oxide, the oxide
solid solution, and the oxide complex contains copper element, at least
one element selected from the group A consisting of strontium, barium,
calcium, and lead, and at least one element selected from the group B
consisting of tungsten, niobium, and tantalum.
In a preferred embodiment, the content of a copper oxide component in the
insulated layer is in the range of 0.3% to 5% by weight in terms of CuO.
In a preferred embodiment, the ceramic substrate comprises a complex oxide
or an oxide solid solution containing copper element and at least one
component excluding copper element.
A method for producing a ceramic substrate for electronic circuit comprises
the steps of:
preparing a complex oxide or an oxide solid solution containing copper
element and at least one component excluding copper element by reacting a
copper oxide with at least one component excluding copper element;
forming ceramic green sheets comprising the complex oxide or the oxide
solid solution and a binder;
patterning a conductive layer comprising a binder and a copper oxide or an
oxide mainly containing copper element on the ceramic green sheets;
laminating a plurality of the ceramic green sheets to form a laminated
body;
heating the laminated body in air so as to burn out the binder comprised in
the ceramic green sheets and the conductive layer;
heating the laminated body, in which the binder has been burnt out, in a
reducing gas to reduce and metallize the conductive layer; and
firing the laminated body, in which the conductive layer has been
metallized, in an inert gas atmosphere to sinter the ceramic green sheets
and the conductive layer.
A method for producing a ceramic substrate for electronic circuit comprises
the steps of:
preparing a complex oxide or an oxide solid solution containing copper
element and at least one component excluding copper element by reacting a
copper oxide with at least one component excluding copper element;
patterning a conductive layer comprising a binder and a copper oxide or an
oxide mainly containing copper element as its main component on a sintered
ceramic substrate;
forming at least one insulated layer on the sintered ceramic substrate
having the conductive layer so as to cover a portion of the conductive
layer, the insulated layer comprising a binder, and the complex oxide or
the oxide solid solution;
patterning another conductive layer comprising a binder and a copper oxide
or an oxide mainly containing copper element at least on the insulated
layer;
heating the sintered ceramic substrate having the conductive layers and the
insulated layer in air so as to burn out the binder comprised in the
conductive layers and the insulated layer;
heating the sintered ceramic substrate, in which the binder has been burnt
out, in a reducing gas to reduce and metallize the conductive layers; and
firing the sintered ceramic substrate, in which the conductive layers has
been metallized, in an inert gas atmosphere to sinter the conductive
layers and the insulated layer.
Thus, the invention described herein makes possible the objective of
providing a highly reliable ceramic substrate for electronic circuit which
prevents defects caused by the partial diffusion of the copper oxide to
the ceramic layer or the insulated layer from the conductive layer.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention may be better understood and its numerous objects and
advantages will become apparent to those skilled in the art by reference
to the accompanying drawings as follows:
FIG. 1a is a view showing the configuration of a ceramic substrate for
multilayer electronic circuit in Example 1.
FIG. 1B is a perspective view of the ceramic substrate for multilayer
electronic circuit in Example 1.
FIGS. 2A, 2B and 2C are views showing the process for producing a ceramic
substrate for printed electronic circuit in Example 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A ceramic substrate for electronic circuit of the present invention can
form two kinds of configurations. One of them is a ceramic substrate for
multilayer electronic circuit in which a conductive layer is patterned on
a ceramic layer. The other one is a ceramic substrate for printed
electronic circuit in which conductive layers patterned and an insulated
layer are laminated on a ceramic substrate.
In the ceramic substrate for multilayer electronic circuit, the ceramic
layer comprises a complex oxide or an oxide solid solution containing
copper element and at least one component excluding copper element, and
the conductive layer comprises copper or an alloy containing copper as its
main component. The ceramic substrate for multilayer electronic circuit is
characterized by the ceramic layer.
In the ceramic substrate for printed electronic circuit, the insulated
layer comprises a complex oxide or an oxide solid solution containing
copper element and at least one component excluding copper element, and
the conductive layer comprises copper or an alloy containing copper as its
main component. The ceramic substrate for printed electronic circuit is
characterized by the insulated layer.
The ceramic layer or the insulated layer of the ceramic substrate for
electronic circuit according to the present invention entirely comprises a
complex oxide or an oxide solid solution containing copper element and at
least one component excluding copper element. Examples of the component
excluding copper element include strontium, barium, calcium, lead,
tungsten, niobium, tantalum, alumina and a material containing an ordinary
vitreous component and the like. In particular, the complex oxide or the
oxide solid solution containing at least one element selected from the
group A consisting of strontium, barium, calcium, and lead; at least one
element selected from the group B consisting of tungsten, niobium, and
tantalum; and copper element is preferred because of a high insulation
property and the formation of a perovskite structure.
Instead of the above-mentioned complex oxide or oxide solid solution, the
ceramic layer or the insulated layer can comprise an oxide complex
containing the above-mentioned complex oxide and/or oxide solid solution
as its components.
Moreover, it is preferred that the content of the copper oxide component in
the ceramic layer or the insulated layer is in the range of 0.3 to 5.0% by
weight in terms of CuO.
Furthermore, it is preferred that the ceramic substrate in the ceramic
substrate for printed electronic circuit comprises a complex oxide or an
oxide solid solution containing copper element and at least one component
excluding copper element, since the ceramic substrate for electronic
circuit using such a ceramic substrate can provide a hybrid IC.
When the ceramic layer of the ceramic substrate for multilayer electronic
circuit is formed from, what is called, a ceramic green sheet obtained by
applying a casting comprising the complex oxide or the oxide solid
solution containing copper element and at least one component excluding
copper element, a binder, and a solvent on an organic film; drying the
casted ceramic green sheet, and removing the organic film, the conductive
layer which is patterned on the green sheet and the ceramic layer can be
simultaneously fired. Thus, it is preferred that the ceramic layer is
formed of the ceramic green sheet. As an ordinary method, a plasticizer
such as dibutyl phthalate or the like can be comprised in the ceramic
green sheet. The ceramic green sheet can be applied to the insulated layer
or the ceramic substrate in the case of the ceramic substrate for printed
electronic circuit.
Moreover, when the conductive layer is formed on the ceramic green sheet, a
procedure, in which the conductive layer is patterned by using printing
ink containing a copper oxide or an oxide mainly containing copper
element, a binder, and a solvent, is effective and preferred.
Examples of a binder material comprised in the green sheet include a
butyral resin and an acrylic resin. Examples of a binder material
comprised in the printing ink include ethyl cellulose and an acrylic
resin.
The binder comprised in the ceramic green sheet and the conductive layer is
preferably burned out by heating at a temperature of 350.degree. to
700.degree. C. in air for 30 minutes to 10 hours.
When the patterned conductive layer is reduced to be metallized, this
portion is heated in a reducing gas. Examples of reducing gases include
hydrogen gas or carbon monoxide gas. Hydrogen gas is preferred in terms of
cost and safety. The reducing conditions are preferably a temperature in
the range of 160.degree. to 550.degree. C.
The green sheets and the conductive layer are fired in an inert gas
atmosphere. Inert gas such as nitrogen gas or argon gas whose low partial
pressure of oxygen is in the range of 10.sup.-6 to 10.sup.-3 arm is
preferably used for this firing. Among the above-mentioned inert gases,
nitrogen gas is particularly preferred from the industrial point of view
because of inexpensiveness.
The firing conditions are different depending on the various kinds of
ceramic materials and on the shapes of the ceramic substrate for
electronic circuit and therefore cannot be generally described. For
example, the firing temperature is in the range of 700.degree. to
1,000.degree. C. (normally at about 900.degree. C.) when lead containing
perovskite is used.
According to the ceramic substrate for electronic circuit having the
conductive layer comprising copper or an alloy containing copper as its
main component, the ceramic layer in the case of the substrate for
multilayer electronic circuit or the insulated layer in the case of the
substrate for printed electronic circuit comprise a copper element. This
copper element does not exist as a metal or as an oxide containing copper
element alone but as a complex oxide or an oxide solid solution containing
copper element and at least one component excluding copper element. Thus,
the diffusion rate of the copper oxide from the conductive layer to the
ceramic layer or the insulated layer becomes low. Moreover, even though
the copper oxide is diffused, a certain degree of copper oxide component
is entirely comprised in the ceramic layer or the insulated layer, so that
a great difference in the firing state between the portion in which the
copper oxide is diffused and the portion in which the copper oxide is not
diffused is not caused, whereby defects are not likely to occur.
The above-mentioned construction can be achieved by using a complex oxide
or an oxide solid solution containing copper element and at least one
component excluding copper element obtained by reacting the copper oxide
with at least one component excluding copper element as a starting
material for the ceramic layer or the insulated layer.
Moreover, according to the production method comprising the above-mentioned
step, when the conductive layer comprising the copper oxide or the oxide
mainly containing copper element is reduced at a low temperature, the
copper oxide or the oxide mainly containing copper element of the
conductive layer alone can be selectively reduced. The copper oxide
component (which is comprised in the complex oxide or the oxide solid
solution) of the ceramic layer or the insulated layer is not readily
reduced compared with the copper oxide or the oxide mainly containing
copper element which is comprised in the conductive layer, so that the
conductive layer alone can be reduced to be metallized in an appropriate
period of treating time. Because of this, the ceramic layer or the
insulated layer can maintain its characteristics without decreasing the
insulation property.
Moreover, the ceramic substrate for electronic circuit of the present
invention regulates the diffusion rate of the copper oxide from the
conductive layer to the ceramic layer or the insulated layer. Even though
the diffusion occurs, a great difference in the firing state between the
portion in which the copper oxide is diffused and the portion in which the
copper oxide is not diffused is not caused, so that the reliability of the
ceramic substrate for electronic circuit having the conductive layer
comprising copper or an alloy containing copper as its main component can
be improved.
EXAMPLES
The present invention will be described by way of illustrating examples
below.
EXAMPLE 1
A ceramic substrate for multilayer electronic circuit will be illustrated
with reference to FIGS. 1A and 1B.
First, each starting materials having a ceramic composition shown below
were mixed and calcinated at 1,050.degree. C. for 2 hours to obtain a
complex oxide. Then, ceramic green sheets were prepared by the ordinary
method using a butyral resin and the raw material obtained by grinding the
complex oxide.
Predetermined patterns for respective conductive layers 1, 2, 3, 4 were
printed on the ceramic green sheets 5 with an electrode paste containing a
copper oxide and an ethyl cellulose resin. Four resulting ceramic green
sheets and four ceramic green sheets 5 were laminated as shown in FIG. 1A
to obtain a laminated body. The laminated body was heated at a temperature
of 480.degree. C. in air for 8 hours to burn out the binder comprised in
the ceramic green sheets and the conductive layer.
The laminated body in which the binder was burnt out was reduced at a
temperature of 220.degree. C. in hydrogen gas for 16 hours, whereby the
pattern of the conductive layer was reduced so as to become metallized.
Then, the laminated body was fired at a temperature of 960.degree. C. in an
atmosphere of nitrogen gas containing 30 ppm of oxygen for 80 minutes,
thereby obtaining a sample. As shown in FIG. 1B, the fired sample had an
outer configuration of 40 mm .times. 40 mm .times. 2 mm, and had a
construction in which 4 conductive metal layers 6 having a width of 10 mm
and a thickness of 4 .mu.m in the center were crossed each other with the
ceramic layer 7 having a thickness of 120 .mu.m sandwiched therebetween.
At the ends of the laminated body, terminal electrodes 8 drawn out of the
respective conductive layers were provided. Ten samples for each ceramic
composition were obtained. The following evaluations of these ten samples
were conducted.
As one evaluation of the reliability of the laminated body thus produced, a
DC voltage of 1,200 V was applied between the terminal electrodes of the
samples, whereby the number of dielectric breakdowns were examined. As
another evaluation of the reliability, other samples produced by the same
method as the above were kept in an air-conditioned bath containing 85%
water vapor at 85.degree. C. for 500 hours. After that, the samples were
allowed to stand for 10 hours so as to dry the surface thereof. A DC
voltage of 120 V was applied to each of the resulting samples, which were
then examined for insulation resistance by using an insulation resistance
tester. The samples having a resistance of 10.sup.7 .OMEGA. or less was
determined as defective defects.
Moreover, the ceramic layers of the fired samples were analyzed by a powder
X-ray method, whereby the presence of e metallic copper phase, CuO phase,
or Cu.sub.2 O phase was confirmed.
The six following kinds of the ceramic layer compositions were produced and
tested.
______________________________________
A: Sr.sub.0.5 Ca.sub.0.5 (Cu.sub.1/4 Nb.sub.3/4).sub.0.05 (Mg.sub.1/3
Nb.sub.2/3).sub.0.90
(Zn.sub.1/2 W.sub.1/2).sub.0.05 O.sub.3 + 2 wt % LiF
B: Pb.sub.0.65 Ca.sub.0.40 (Cu.sub.2/5 W.sub.3/5).sub.0.06 (Mg.sub.1/3
a.sub.2/3).sub.0.90
(Ni.sub.1/2 W.sub.1/2).sub.0.05
C: Pb.sub.0.55 Ba.sub.0.50 (Mg.sub.1/3 Ta.sub.2/3).sub.0.05 (Ni.sub.1/3
Nb.sub.2/3).sub.0.80
(Mg.sub.1/2 W.sub.1/2).sub.0.15 O.sub.3
D: Pb.sub.0.55 Sr.sub.0.20 Ca.sub.0.30 (Cu.sub.1/3 Nb.sub.2/3).sub.0.50
Zr.sub.0.30
(Mg.sub.1/3 Ta.sub.2/3).sub.0.20 O.sub.3
E: Al.sub.2 O.sub.3 55 mol %, SiO.sub.2 20 mol %, MgO 10 mol %,
ZnO 10 mol %, Li.sub.2 O.sub.3 3 mol %, CuO.sub.2 2 mol %
F: Al.sub.2 O.sub.3 70 mol %, SiO.sub.2 5 Mol %, Cu.sub.2 O 15 mol %,
CaF.sub.2 10 mol %
______________________________________
C, D, and F are ceramic compositions prepared for comparative examples.
The composition of the ceramic layer, the number of dielectric breakdowns,
and the number of resistance defects are shown in Table 1.
TABLE 1
______________________________________
Presence of
a metallic
copper phase,
Number of
Number of
Sample CuO phase, insulation
resistance
No. Composition
or Cu.sub.2 O phase
defects defects
______________________________________
1 A None 0 0
2 B None 0 0
3 C None 3 7
4 D Cu.sub.2 O phase
2 5
and CuO phase
are present
5 E None 1 1
6 F Metallic copper
10 10
phase is present
______________________________________
In Table 1, it was confirmed by an X-ray microanalyzer that in the case of
Sample No. 3, the copper element was not entirely comprised in the ceramic
layer and the copper element was diffused in the vicinity of the portion
which was in contact with the conductive layer. When the cross section was
observed by microscope, it was found that many defects were caused in the
vicinity of the boundary between the portion in which the copper element
was diffused and the portion in which the copper element was not diffused.
It was confirmed by an X-ray diffraction analysis of the ceramic layer that
in the case of Sample Nos. 4 and 6, a copper metal and an oxide containing
copper element alone were present.
On the other hand, in the case of Sample Nos. 1, 2 and 5 of the ceramic
substrate for electronic circuit according to the present invention in
which the ceramic layer entirely comprises a copper element, and the
copper element does not exist as a metal or an oxide containing copper
element alone but as a complex oxide or an oxide solid solution containing
copper element and at least one component excluding copper element, the
insulation property of the ceramic layer was maintained and excellent
characteristics having few insulation defects and resistance defects were
obtained.
EXAMPLE 2
A ceramic substrate for printed electronic circuit will be illustrated with
reference to FIGS. 2A, 2B and 2C.
First, 96% alumina-calcia-silica sintered substrate was used as a ceramic
substrate 9. A predetermined pattern for the conductive layer 10 was
printed on the ceramic substrate 9 with an electrode paste containing a
copper oxide, an ethyl cellulose resin and borosilicate zinc glass (FIG.
2A). Each starting materials for the insulated layer having a ceramic
composition shown below were mixed and calcinated at a temperature of
1,050.degree. C. for 2 hours to obtain a complex oxide. An insulated ink
was prepared by the ordinary method using an ethyl cellulose resin and the
raw material obtained by grinding the complex oxide. The insulated layer
12 was formed with the insulated ink so as to cover at least one portion
of the conductive layer 10 (FIG. 2B). Further, another conductive layer 11
was patterned at least on the insulated layer 12 (FIG. 2C).
The ceramic substrate having the conductive layers 10, 11 and the insulated
layer 12 was heated at a temperature of 500.degree. C. in air for 30
minutes to burn out the binder.
The sintered ceramic substrate 9 having the conductive layers 10, 11 and
insulated layer 12 in which the binder was burnt out was reduced at a
temperature of 220.degree. C. in hydrogen gas for 16 hours, whereby the
conductive layers was metallized. After that, the resulting ceramic
substrate was fired at a temperature of 820.degree. C. in an atmosphere of
nitrogen containing 70 ppm of oxygen for 6 minutes, thereby obtaining a
sample. Fifty samples for each ceramic composition were obtained. The
following evaluations of these fifty samples were conducted.
The fired sample comprised the ceramic substrate 9 having a dimension of 40
mm .times. 40 mm .times. 1 mm, and had a construction in which 2
conductive metal layers 10, 11 having a width of 10 mm and a thickness of
4 .mu.m in the center were crossed each other with the insulated layer 12
having a thickness of 55 .mu.m therebetween.
As one evaluation of the reliability of the sample thus produced, a DC
voltage of 250 V was applied between the terminal electrodes of the
samples, whereby the number of dielectric breakdowns were examined. The
upper conductive layer was removed by polishing, and the insulated layer
in the fired sample was analyzed by the powder X-ray method to confirm the
presence of a metallic copper phase, CuO phase or Cu.sub.2 O phase.
The six following kinds of the insulated layer compositions were produced
and tested.
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G: Sr.sub.0.5 Ca.sub.0.5 (Cu.sub.1/4 Nb.sub.3/4).sub.0.05 (Mg.sub.1/3
Nb.sub.2/3).sub.0.90
(Zn.sub.1/2 W.sub.1/2).sub.0.05 O.sub.3 + 2 wt % LiF
H: Pb.sub.0.65 Ca.sub.0.40 (Cu.sub.2/5 W.sub.3/5).sub.0.06 (Mg.sub.1/3
a.sub.2/3).sub.0.90
(Ni.sub.1/2 W.sub.1/2).sub.0.05
I: Pb.sub.0.55 Ba.sub.0.50 (Mg.sub.1/3 Ta.sub.2/3).sub.0.05 (Ni.sub.1/3
Nb.sub.2/3).sub.0.80
(Mg.sub.1/2 W.sub.1/2).sub.0.15 O.sub.3
J: Pb.sub.0.55 Sr.sub.0.20 Ca.sub.0.30 (Cu.sub.1/3 Nb.sub.2/3).sub.0.50
Zr.sub.0.30
(Mg.sub.1/3 Ta.sub.2/3).sub.0.20 O.sub.3
K: Al.sub.2 O.sub.3 55 mol %, SiO.sub.2 20 mol %, MgO 10 mol %,
ZnO 10 mol %, Li.sub.2 O 3 mol %, CuO 2 mol %
L: Al.sub.2 O.sub.3 70 mol %, SiO.sub.2 5 mol %, Cu.sub.2 O 15 mol %,
CaF.sub.2 10 mol %
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I, J, and L are ceramic compositions prepared for comparative examples.
The composition of the insulated layer and the number of dielectric
breakdowns are shown in Table 2.
TABLE 2
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Presence of
a metallic
copper phase,
Number of
Sample CuO phase, insulation
No. Composition or Cu.sub.2 O phase
defects
______________________________________
7 G None 2
8 H None 0
9 I None 13
10 J Cu.sub.2 O phase
8
and CuO phase
are present
11 K None 2
12 L Metallic copper
19
is present
______________________________________
In Table 2, it was confirmed by an X-ray microanalyzer that in the case of
Sample No. 9, the copper element was not entirely comprised in the
insulated layer and the copper element was diffused in the vicinity of the
portion which was in contact with the conductive layer. When the cross
section of the sample was observed by microscope, it was found that many
defects were caused in the vicinity of the boundary between the portion in
which the copper element was diffused and the portion in which the copper
element was not diffused.
It was confirmed by an X-ray diffraction analysis of the insulated layer
that in the case of Sample Nos. 10 and 12, a copper metal and an oxide
containing copper element alone were present.
On the other hand, in the case of Sample Nos. 7, 8 and 11 in which the
insulated layer entirely comprises a copper element, and the copper
element does not exist as a metal or an oxide containing copper element
alone but as a complex oxide or an oxide solid solution containing copper
element and at least one component excluding copper element, the
insulation property of the insulated layer was maintained and excellent
characteristics having few insulation defects and resistance defects were
obtained.
EXAMPLE 3
A ceramic substrate for printed electronic circuit which is similar to that
of Example 2 will be illustrated.
Each sintered substrate having a composition shown in Table 3 was used as a
ceramic substrate. The ceramic composition of the insulated layer of
Sample No. 8 in Example 2 was used for that of the insulated layer. That
is, the composition which was used was Pb.sub.0.65 Ca.sub.0.40 (Cu.sub.2/5
W.sub.3/5).sub.0.06 (Mg.sub.1/3 Ta.sub.2/3).sub.0.90 (Ni.sub.1/2
W.sub.1/2).sub.0.05 O.sub.3.05.
The same procedure as that of Example 2 was repeated. Fifty samples for
each ceramic composition were obtained. The following evaluations of these
fifty samples were conducted.
As one evaluation of the reliability of the sample thus produced, a DC
voltage of 250 V was applied between the terminal electrodes of the
samples, whereby the number of dielectric breakdowns were examined. As
another evaluation of the reliability, an adhesive tape was attached to
the conductive layers, and the contacting state between the conductive
layers and the ceramic substrate was observed after the adhesive tape was
removed.
The composition of the ceramic substrate, the number of insulation defects,
and the number of samples in which the conductive layer was peeled by 1 mm
or more are shown in Table 3.
The composition of the ceramic substrate of Sample No. 14 is that of a
comparative example.
TABLE 3
______________________________________
Number of
Sample
Composition insulation
Number of
No. of substrate defects peeled samples
______________________________________
13 Baked substrate 0 2
in which 0.84%
by weight of CuO
is added to 96%
alumina--magnesia--
silica
14 Baked substrate 9 2
in which 15.9%
by weight of CuO
is added to 96%
alumina--magnesia--
silica
______________________________________
In Table 3, the metallic copper and copper oxide were not detected in the
ceramic substrate of Sample No. 13 by the powder X-ray diffraction.
However, Cu.sub.2 O was detected in the ceramic substrate of Sample No.
14. Because of this, it was stipulated that in Sample No. 14, the
insulation defects which caused problems before the peeling test were
generated. It was found by examining the conductive layers of Sample Nos.
13 and 14 by the powder X-ray diffraction and fluorescence X-ray analysis
that the conductive layers comprised about 3% by weight of metallic lead
based on the total weight of metallic copper.
As is apparent from Table 3 and the above-mentioned results, a copper
element is comprised in the ceramic substrate having the conductive layers
and the insulated layer, in which the copper element does not exist as a
metal or an oxide containing copper element alone but as a complex oxide
or an oxide solid solution which contains copper element and at least one
component excluding copper element. In the ceramic substrate for
electronic circuit having such a ceramic substrate, the conductive layers
have an improved adhesion with respect to the ceramic substrate compared
with a ceramic substrate in which the complex oxide or the oxide solid
solution is not comprised.
EXAMPLE 4
A ceramic substrate for multilayer electronic circuit similar to that of
Example 1 will be illustrated.
First, as a composition for the ceramic layer, the composition in which CuO
of a predetermined amount shown in Table 4 was added to a main component
of each oxide shown below was prepared, followed by calcination at
1,050.degree. C. for 2 hours. The material obtained by grinding the
resulting mixture and a butyral resin were mixed together with an organic
solvent to prepare a ceramic green sheet having a thickness of 150 .mu.m
using a doctor blade method. A sample was obtained by using this ceramic
green greet in the same way as in Example 1. Ten samples for each ceramic
composition were obtained. The following evaluations of these ten samples
were conducted.
The evaluations for reliability of the samples were conducted by the
ordinary method in the same way as in Example 1. In addition, as severe
conditions, the number of dielectric breakdowns was examined by applying a
DC voltage of 2,000 V between the terminal electrodes of the samples.
Other samples were kept in a saturated water vapor of 125.degree. C. for
500 hours. After that, the samples were allowed to stand in air for 10
hours so as to dry the surface thereof. A DC voltage of 250 V was applied
to each of the resulting samples, which were then examined for insulation
resistance by using an insulation resistance tester. The samples having a
resistance of 10.sup.7 .OMEGA. or less were determined as defective.
The following compositions M and N were used as a main component for the
ceramic layers.
M: Pb.sub.1.005 (Mg.sub.1/3 Nb.sub.2/3).sub.0.9 (Ni.sub.1/2
W.sub.1/2).sub.0.1 O.sub.3.005
N: Al.sub.2 O.sub.3 90 wt % SiO.sub.2 8 wt % CaF.sub.2 2 wt %
The added amount of the copper oxide was of five kinds, ranging from 0.1 to
40% by weight based on the total weight.
The main component of the ceramic layer, the number of dielectric
breakdowns, and the number of resistance defects are shown in Table 4.
TABLE 4
__________________________________________________________________________
under the under the
Content
ordinary conditions
severe conditions
Main of CuO
Insulation
Resistance
Insulation
Resistance
Sample No.
Component
wt % defects
defects
defects
defects
__________________________________________________________________________
15 M 0.1 0 0 2 1
16 M 0.3 0 0 0 0
17 M 1.5 0 0 0 0
18 M 5.0 0 0 0 0
19 M 7.0 0 1 0 3
20 N 0.1 0 0 3 0
21 N 0.3 0 0 0 0
22 N 1.5 0 0 0 0
23 N 5.0 0 0 0 0
24 N 7.0 0 1 0 6
__________________________________________________________________________
In Table 4, either CuO, Cu.sub.2 O, or copper oxide was not present in each
sample by the X-ray diffraction. Under the ordinary conditions, almost no
defects were caused in any samples. However, under severe conditions, when
the content of CuO was less than 0.3% by weight, the insulation defects
were likely to appear because of the defects in the ceramic layer caused
by the partial diffusion of the copper oxide. When the content of CuO was
more than 5% by weight, the resistance defects were likely to appear
because of the resistance decrease of the ceramic layer itself. Thus, when
the content of CuO was in the range of 0.3 to 5% by weight, more
preferable characteristics were obtained.
EXAMPLE 5
A ceramic substrate for printed electronic circuit which is similar to
Example 2 will be illustrated.
As the ceramic substrate, 96% alumina-calcia-silica sintered substrate
similar to that of Example 2 was used.
As a starting material for the insulated layer, a powder obtained by adding
CuO of a predetermined amount shown in Table 5 to the same main component
as that of Example 4, followed by calcination and grinding was used. A
sample was obtained in the same way as in Example 2. Fifty samples for
each ceramic composition were obtained. The following evaluations of these
fifty samples were conducted. In order to examine the reliability of the
samples, a DC voltage of 250 V was applied to the samples to examine the
number of dielectric breakdowns in the same as in Example 2. In addition,
as a severe testing, a DC voltage of 500 V was applied to examine the
number of dielectric breakdowns.
The composition of the insulated portion and the number of dielectric
breakdowns obtained when 50 samples were tested ere shown in Table 5.
TABLE 5
______________________________________
Dielectric
Dielectric
Content breakdown
breakdown
Main of CuO defects defects
Sample No.
Component wt % at 250V at 500V
______________________________________
25 M 0.1 1 4
26 M 0.3 0 0
27 M 1.5 0 0
28 M 5.0 0 0
29 M 7.0 2 12
30 N 0.1 2 8
31 N 0.3 1 0
32 N 1.5 0 0
33 N 5.0 0 0
34 N 7.0 3 16
______________________________________
In Table 5, either CuO, Cu.sub.2 O, or copper oxide was not present in each
sample by the X-ray diffraction. Under the ordinary conditions, almost no
defects were caused in any samples. However, under severe conditions, when
the content of CuO was less than 0.3% by weight or more then 5% by weight,
the insulation defects were likely to appear. Thus, when the content of
CuO was in the range of 0.3 to 5% by weight, more preferable
characteristics were obtained.
As described above, according to the present invention, the ceramic
substrate for electronic circuit comprises the ceramic layer in the case
of the substrate for multilayer electronic circuit or the insulated layer
in the case of the substrate for printed electronic circuit which entirely
comprises a complex oxide or an oxide solid solution containing copper
element and at least one component excluding copper element. Moreover, a
method for producing this kind of ceramic substrate for electronic circuit
comprises the steps of: patterning the conductive layer with a copper
oxide or an oxide mainly containing copper element for the purpose of
preventing the binder from being insufficiently burnt out; reducing only
the conductive layer at a low temperature to metallize it after burning
out the binder in air; and firing it in an inert gas atmosphere. In the
conventional ceramic substrate for electronic circuit in which the copper
oxide is generated on the conductive layer in the course of the firing,
the copper element is partially diffused into the ceramic layer or the
insulated layer, and defects are caused due to the difference in the
firing state between the portion in which the copper element is diffused
and the portion in which the copper element is not diffused. Thus, the
present invention eliminates the defects caused in the conventional
ceramic substrate for electronic circuit. Moreover, the present invention
is effective in providing a highly reliable ceramic substrate for
electronic circuit.
It is understood that various other modifications will be apparent to and
can be readily made by those skilled in the art without departing from the
scope and spirit of this invention. Accordingly, it is not intended that
the scope of the claims appended hereto be limited to the description as
set forth herein, but rather that the claims be construed as encompassing
all the features of patentable novelty that reside in the present
invention, including all features that would be treated as equivalents
thereof by those skilled in the art to which this invention pertains.
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